We want to investigate the principles that control expression of the yellow gene in development of Drosophila melanogaster. This gene is involved in melanin formation and pigmentation of the adult cuticle, and its expression may be under developmental, perhaps hormonal, control like other enzymes in the pathway of insect cuticle formation. Although the gene is genetically very well characterized, it has not yet been isolated by molecular cloning, and no RNA or protein product is known. By "chromosome walking", we have cloned DNA fragments that contain yellow coding sequences as defined by breakpoints of three independent yellow deficiencies. These fragments will be used to characterize the yellow gene organization and its mRNA and protein products. We will first analyze the adult epidermis of the late pupal stage; this is the tissue and time the yellow product is required to deposit pigment. Its regulation during development will be studied by establishing a developmental and tissue specific profile. Furthermore, we will analyze by DNA sequencing several Y2 type mutant alleles that give rise to different and distinct patterns of cuticle coloration, and are believed to be regulatory mutants. Our studies will contribute to the understanding of control mechanisms that are responsible for gene regulation in development and differentiation of eukaryotic organisms. In addition, by analyzing unstable alleles that revert to wild-type, or frequently give rise to deletions, we will be able to investigate the behavior of transposable elements and the mechanisms of mutagenesis in higher organisms.